Crystal oscillator circuits



Feb. 16, 1937. v

A. M. ,BRAATEN CRYSTAL OSCILLATOR CIRCUITS I Filed March 19, 1932 2 Shgets-Sheet 1 J2 2 "I g, I 01/1707 INVENTOR AIR/Tag BRAATEN ATTORNEY bulb p A. M. BRAAYTEN Filed March 19, 1932 2 Sheets-Sheet 2 our/ ur INVENTOR ARTHUR M.BRAATEN BY h g ATTORNEY Feb. 16, 1937.

CRYSTAL OSCILLATOR CIRCUITS Patented Feb. 16, 1937 UNITED STATES PATENT OFFICE CRYSTAL OSCILLATOR CIRCUITS of Delaware Application March 19, 1932, Serial'No. 599,952

8 Claims.

' This invention relates --to improved crystal controlled oscillator circuits and is described in greater detail in connection with the accompanying drawings, wherein,

Figure 1 illustrates an oscillatory system formed. of electron discharge devices, resistances and condensers, suitably associated therewith whose frequency of operation is pulled or locked into step by the suitable connection of a piezoelectric or quartz crystal oscillator,

Figure 2 illustrates a system similar to Figure 1 wherein the crystal is connected between the plate and cathode of one of the electron dis charge devices,

Figure 3 illustrates a similar system wherein the crystal is connected across the anode resistance of one of the tubes rather than as illustrated in Figure 1 between the grid and cathode of one of the oscillating tubes or electron discharge devices,

Figure 4 illustrates a system similar to Figure 1 wherein the piezo-electric quartz'crystal is connected between the plates of the oscillating tube arrangement,

Figure 5 illustrates a circuit arrangement similar to Figures 1 to 4 with the suitable connection of the crystal illustrated in Figure 6 at points indicated thereon and wherein for improved operation, utilization is made of screen grid tubes,

Figure 7 is a modification of Figure 1 wherein the system fails to oscillate without the presence of a crystal,

'Figures 8 and 9 are modifications of the system shown in Figure 7, and,

Figure 10 is a further modification of a circuit wherein oscillations depend upon the presence of a piezoelectric crystal.

Turning to-Figure l, the anodes of tubes I, 2 are supplied with anode potential as shown through resistors RI, R2. The anodes and grids of the tubes I, 2 are cross-connected as illustrated-by condensers CI, C2. The grid filament circuits are completed by means of biasing resistors rI, r2.

Assuming that the crystal is removed from this circuit, Figure 1 is then a relaxation oscillator which operates as follows. Suppose, due to some disturbance, such as a minute increase in the voltage on the grid of tube I, the plate current of tube I is increased slightly. The potential drop across RI is increased, causing a decrease in the voltage on the plate of tube I. This change of potential acting through condenser CI will cause a reduction in the voltage on the grid of tube 2. As a result of this decrease of potential on the grid the plate current will decrease, causing a decrease in the potential drop across R2. A corresponding increase in the voltage on the plate of tube 2 takes place. Due to the amplifying properties of the tubes, the 5. increase in plate voltage of tube 2 is much greater than the decrease in plate voltage of tube I. This increased potential acts through condenser C2 to increase the Voltage on the grid of tube I. A corresponding decrease of the 10 plate potential of tube I takes place, making the grid of tube 2 still more negative, which causes the grid of tube 5 to go still more positive. This cycle of events continues until the potential on the grid of tube 2 goes below cutoff; the plate 1'5 current in tube 2 then becomes zero. Since there is now no current to maintain charges on condensers CI and C2 they will discharge through T2 and H or RI and R2, respectively.- During the discharge period the potential on the grid of 20 tube 2 builds up until plate current again. begins to flow, the cycle of events described above now being repeated, but in the opposite direction. The alternate discharges of the two tubes con. tinue as long as energy is'supplied to them from 25 the battery sources. The frequency of the discharges can be controlled by. varying the values of either thecondensers or the resistors, or both.

According to my invention, I- adjust the circuit so that the frequency of oscillation is the 30 same, or very nearly so, as the resonant frequency of the crystal. Then, when the crystal is connected in the circuit, as shown above, an alternating voltage corresponding to the potential on the grid of tube l is applied across its .5 electrodes. The crystal is set in vibration, and, due to the piezo-electric action, applies a voltage to the grid which is very nearly in phasewith the potential supplied from tube 2. As the frequency of oscillation of the multivibrator is 9 readily influenced by a small applied voltage or nearly the same frequency, the multivibrator will be locked into step with the crystal and its frequency will therefore be controlled thereby. 45 In the arrangement shown in Figure 2, the crystal is connected from plate to filament or from anode to cathode of one of the tubes here shown between the plate and cathode of tube 2 although it should be clearly understood that the 50 crystal could be connected across the plate and cathode of tube I. Similarly, reverting for the present to Figure 1, the quartz crystal indicated QC could be connected across the resistor 1'2' 7 equally as well. 55

- and 2 but as illustrated in Figure 3 may be placed bilizes the frequency of operation ofthe circuit across one of the anode resistors of oneof the tubes, and as illustrated in Figure 4 may be connected between the plates of tubes'I and 2.

Figure 5, of course, illustrates the'multivibrator Y system shown in Figures 1 to 4 with the exception that the tubes I, 2 are of the screen'grid type thereby preventing undesired feed back through the tube and insuring still higher frequency stability and accuracy. In the arrangement shown in Figure 5 the system, of course, is self oscillatory and is locked into step with the crystal illustrated in Figure fi provided the crystal connection of Figure 6 is placed across the points XY of resistance RI, or, across the points XY of resistance R2, or, across the plate connection pointsXX of tubes I and 2, or, across the grid connection points XX of tubes I and 2, or, across the points XY in the grid circuit of either tube,

, or, between the plate point X of either tube and the grounding pointY of the corresponding tube.

, In the system so far described it is 'to be noted that both tubes comprise an oscillator neither one being able to function without the other. That is to say, the circuit will oscillate without the crystal in circuit. Addition of the crystal into circuit, according to my present invention, stawhich otherwise is very unstable. Neither tube can be properly called the oscillator in the systerns shown in Figures 1 to 5 since the crystal may be placed in the circuit of either tube with identical result. This feature has already been pointed out to some extent.

By proper proportioningof the circuit elements, or in other words, the electrical constants of the various elements involved in Figures 1 to 5, a.

decidedly different 'mode of operation can be reached with identical circuits. In the latter case, the circuits can be so arranged that they will not oscillate without the crystal in circuit. But once the crystal is placed in the circuit both tubes operate as an oscillator at a frequency determined by the piezo-electric crystal.

Thus, by discreet choice of values for the condensers CI, C2, that is to say by making them suffioiently small the circuit shown in Figure '7 which is otherwise identical to that shown in Figure l, with the possible exception of condenser C3, operates in an altogether different fashion than the circuit shown in Figure 1.

That is to say, condensers CI and C2 are made small so that the circuit will not generate relaxation oscillations. Consequently, tubes I and 2 form a resistance coupled amplifier with feed back through condenser C2, condenser C2re turning energy to the crystal from tube 2 in proper phase to sustain oscillations of the crystal. Here again, the crystal may be connected across TI, across T2 or between the grids of the tubes as illustrated in Figure 8, or between plate and grid of the tubes as illustrated in Figure 9.

Condenser C3 of Figure '7 acts merely as an adjustment for the crystal frequency which may also be accomplished by varying the spacing of r the crystal electrodes from the crystal.

In Figure 8 one of the possible connections ala ready referred to for the crystal in the circuit of Figure '7 is illustrated. The crystal in Figure 8 is connected between the grids oftubes I and 2 and in Figure 9 it is illustrated as being connected between the plate of tube 2 and the grid of tube I.

Output from the oscillator is taken as indicated by the arrows on the various circuits. 1 In Figure 1 it is taken from, for examplegtheplate and filament of tube 2, in Figure 2 from across the plate resistor R2 of tube 2, in Figure 4 from the plate and cathode of tube l, and similarly so in Figure 5. In Figure 7 output energy is taken from resistor R2 of tube 2. The output'is similarly taken from resistor R2 of Figure 8, andin Figure 9 output ener y is taken from across resistor RI of tube I.

The output energy being of'constant frequency may be utilized in various ways. It maybe fed to an amplifier, then frequency multiplied, modulated, power amplified, and finally radiated .in" the form of electromagnetic wave energy. f Or the output energy of my improved oscillating 'cir-' cuits may be combined with received incoming electromagnetic waves to produce an intermedi ate frequency wave which in turn may be demodulated to produce a transmitted signal. Or, the outputs of my improved oscillating circuits may be used in frequency measuring apparatus, the beatbetween my oscillator and an unknown fre quency source indicating the frequency of the unknown source inasmuch as it is assumed that the frequency of my oscillating source is known beforehand.

Further, in connection with Figure denser C3 serves merely as an adjustment for the crystal frequency despite the fact that it is connected between the plates of the tubes rather than across the crystal itself. V

In Figure 9, it is to be noted that the quartz crystal replaces one of the condensers, namely condenser C2, in Figure 8, and condenser C3 has been omitted. In the arrangement shown in Figure 9 the quartz crystal acts as a highly discriminating feed back circuit feeding back energy for oscillation generation only of a frequencycorresponding to the natural frequency of the crystal.

In the arrangement shown in Figure 10, the

crystal is connected between the plate and grid of one of the tubes. As before, condenser C3 is used for varying the operating frequency. This circuit, I have found, will not oscillate unless the crystal is present.

oscillatory system comprising a plurality of electron discharge devices, each having an anode-a cathode and a control grid, a resistor connected between the control grid and cathode of each of said devices,- a resistor connected between the anode and cathode of each of said devices,'con- 'densersinterconnecting the anode of one device to the grid of another device, and,"a resonant system of substantially constant frequency con nected directly across two of the electrodes of one of said devices.

2. An oscillatory system comprising an electron discharge device having a plurality of electrodes including an anode, a cathode, and a control grid, another electron discharge device having a plurality of electrodes including an anode, a cathode, and a control grid, resistances connected between the control grids and cathodes of said devices, resistances connected between the anodes and cathodes of said devices, a condenser connected from the anode of one of said devices to the control grid of another of said devices, a condenser connected from the control grid of said other device to the anode of said one device, and, an electromechanical vibrator in the form of a piezo-electric quartz crystal connected between two dissimilar electrodes of said devices, said condensers being so adjusted and of such value in capacitance that the system oscillates without the presence of said quartz crystal and whereby when said quartz crystal is inserted into circuit oscillations in the circuit are synchronized with a resonant frequency of said piezo-electric quartz crystal.

3. An oscillatory system comprising two electron discharge tubes each having an anode, a cathode, and a control electrode, a condenser connecting the control electrode of a first tube to the anode of a second tube, another condenser connecting the anode of the second tube to the control electrode of the first tube, a resistor connected in each of the anode circuits of said tubes, a resistor connected between the control electrode and cathode of each of said tubes, and, a piezoelectric quartz crystal connected directly across one at least of the resistors in said anode circuits.

4. An oscillatory system comprising two electron discharge tubes each having an anode, a cathode, and a control electrode, condensers cross-connecting the anodes and control electrodes of said tubes, a resistance connected be- I tween the anode and cathode of each of said tubes, a resistance connected between the control electrode and cathode of each of said tubes, and, a two electrode piezo-electric quartz crystal connected across the anode and cathode of one of said tubes.

5. An oscillatory system comprising two electron discharge tubes each having an anode, a cathode, and a control electrode, condensers cross-connecting the anodes and control electrodes of said tubes, a resistance connected between the anode and cathode of each of said tubes, a resistance connected between the control electrode and cathode of each of said tubes, and, a two electrode piezo-electric quartz crystal con nected across one at least of the resistances connected between the anode and cathode of said tubes.

6. An oscillatory system comprising two electron discharge tubes each having an anode, a,

cathode, and a control electrode, condensers cross-connecting the anodes and control electrodes of said tubes, a resistance connected between the anode and cathode of each of said tubes, a resistance connected between the control electrode and cathode of each of said tubes, and, a two electrode piezo-electric quartz crystal connected across the anode and control electrode of one of said tubes.

7. An oscillatory system comprising two electron discharge tubes each having an anode, a cathode, a control electrode, capacitive impedances cross-connecting the anodes and control electrodes of said tubes, a resistive impedance in circuit between the anode and cathode of each of said tubes, a resistive impedance in circuit between the control electrode and the cathode of each of said tubes, and a two-electrode piezoelectric device in shunt with one of the two im- ARTHUR M. BRAATEN. 

